Timing mechanism

ABSTRACT

An arming-delay mechanism suitable for use in artillery shells to prevent premature arming and explosion of the shell, employing an escapement including a balance which is &#39;&#39;&#39;&#39;unbalanced&#39;&#39;&#39;&#39; in that its pivot axis is radially further outward than its center of gravity with respect to the spin axis about which the mechanism spins after the shell is fired. It also includes two sequentially operating centrifugal detents for preventing accidental starting of the operation of the timing mechanism prior to firing of the shell, with the balance arranged to serve as an interlock between the two detents whereby the second detent cannot be actuated to its open position until after the first detent has been actuated. Arming is produced, after spinning of the shell releases both detents in sequence, by means of a centrifugally operated rotor having escapement teeth on it, which teeth engage the balance directly rather than through a gear train. The unbalanced balance responds to centrifugal forces produced during spinning to resist motion of the rotor more strongly than a &#39;&#39;&#39;&#39;balanced&#39;&#39;&#39;&#39; balance of the same mass, making possible a smaller, lighter and simpler mechanism for a given amount of delay, and the sequentially operating arrangement of detents provides a high degree of safety from premature accidental arming.

United States Patent Krupa TIMING MECHANISM Thomas J. Krupa,Willingboro, NJ.

Delaware Valley Armaments, Inc., Mount Laurel, NJ.

June 9, 1970 Inventor:

Assignee:

Filed:

Appl. No.: 44,698

Primary Examiner-Samuel W. Engle Attorney-Howson and l-lowson [451 June20, 1972 [57] ABSTRACT An arming-delay mechanism suitable for use inartillery shells to prevent premature arming and explosion of the shell,employing an escapement including a balance which is unbalanced" in thatits pivot axis is radially further outward than its center of gravitywith respect to the spin axis about which the mechanism spins after theshell is fired. It also includes two sequentially operating centrifugaldetents for preventing accidental starting of the operation of thetiming mechanism prior to firing of the shell, with the balance arrangedto serve as an interlock between the two detents whereby the seconddetent cannot be actuated to its open position until after the firstdetent has been actuated. Arming is produced, after spinning of theshell releases both detents in sequence, by means of a centrifugallyoperated rotor having escapement teeth on it, which teeth engage thebalance directly rather than through a gear train. The unbalancedbalance responds to centrifugal forces produced during spinning toresist motion of the rotor more strongly than a balanced balance of thesame mass, making possible a smaller, lighter and simpler mechanism fora given amount of delay, and the sequentially operating arrangement ofdetents provides a high degree of safety from premature accidentalarming.

9 Claims, 16 Drawing Figures PKTENTEDJUMZQ i972 SHEET t (If 4 INVENTOR;THOMAS J. K RUPA ATTYS.

TIMING MECHANISM BACKGROUND OF THE INVENTION Various timing mechanismsare known in the prior-art which are useful, for example, in preventingpremature arming of an explosive shell of the type to which a spinningmotion is imparted as it moves along the muzzle of the gun from which itis fired. Typically, some form of centrifugally operable detent means isemployed normally to prevent motion of the mechaniam from its armedtoward its unarmed condition, and which is responsive to centrifugalforces, generated by spinning of the mechanism after firing of theshell, to free the mechanism and permit it to advance toward its armedposition. Typically also, the driving forces for the timing mechanismare provided by a rotor device pivoted off-center from its center ofmass, and also ofi center from its spin axis, so that the spinning ofthe mechanism causes the rotor to turn after the detent arrangementreleases. The rotational motion of the rotor is typically communicatedthrough a set of gears to an escapement wheel which engages, and causesoscillation of, a balance, the inertia of the balance serving to resistrotation of the escapement wheel and of the rotor, so as to slow theadvance of the rotor from its unarmed to its armed position. By sucharrangements it is intended to provide a relatively long delay between atime when the gun is fired and the time when the shell becomes armed,thereby to prevent premature explosion of the shell. The copendingapplication of Oliver J. Cheney, Ser. No. 833,007, filed June 13, 1969and of common assignee herewith, shows and describes one known fonn ofsuch timing mechanism.

It is desirable to make such a timing mechanism as small, lightweight,compact and simple as possible while reliably providing the desireddelay, and at the same time to reduce the risk of premature arming ofthe mechanism, for exam le due to shocks and vibration occurring priorto firing, during handling or transportation for example. In mostpreviously known systems it is possible for such shocks to release thedetent arrangement, in which case subsequent shocks and vibration orother mechanical effects may advance the timing mechanism toward itsarmed condition, with resultant later premature arming of the mechanism.

Accordingly it is an object of the invention to provide a new and usefultiming mechanism.

Another object is to provide such a timing mechanism which produces anincreased delay time for the same size and mass balance, or the samedelay time with a lighter or smaller balance.

It is also an object to provide such a timing mechanism in whichintermediate gears between the rotor and the balance are eliminated.

A further object is to provide an improved detent arrangement whichreduces the chance of premature undesired release of the detentarrangement.

It is also an object to provide a time-delay mechanism having a newbalance arrangement providing longer delays for a given inertial momentof the balance, and at the same time operating in connection with anarrangement of plural detents to provide greater protection againstpremature accidental detent release.

SUMMARY OF THE INVENTION These and other objects of the invention areachieved by the provision of a centrifugally operable timing mechanismemploying balance means having a pivot axis which is further from thespin axis of the mechanism than is the center of mass of the balancemeans, and further comprising first and second centrifugally operabledetent means for preventing operation of the timing mechanism prior tospinning of the mechanism about its spin axis together with interlockmeans acting between the first and second detent means to restrain thesecond detent means from opening until the first detent means has movedto free the mechanism. While either the unbalanced arrangement of thebalance means or the construction of sequentially operating detent meansmay be employed to advantage by itself without the other, in a preferredform of the invention the balance means is not only unbalanced asdescribed, whereby centrifugal forces acting on the balance means duringspinning of the mechanism provide additional resistance to, and slowingof, the operation of the timing mechanism, but it is also arranged andconfigured to provide the desired interlock action by preventing releaseof the second detent means until operation of the first detent meanspermits the balance means to move so as then to free the second detentmeans. Also in the preferred embodiment, a centrifugally operable rotorwith its center of mass displaced from its pivot axis is used to drivethe balance means directly by means of escapement teeth on the rotor,without intervening gear means.

The abovedescribed construction of balance means increases the timedelay produced by the mechanism, other things being equal, and inpractical applications makes possible reductions in the mass of thebalance and/or elimination of intervening gears between rotor andbalance means; the sequential detent arrangement makes the timingmechanism much less susceptible to premature undesired release, sinceunless the time delay mechanism is spinning as it is after firing of theshell, it would require a plurality of specially timespaced andspecially directed shocks to release the timing mechanism fully, anoccurrence which is extremely unlikely.

BRIEF DESCRIPTION OF FIGURES Other objects and features of the inventionwill be more readily understood from a consideration of the followingdetailed description taken with the accompanying drawings, in which:

FIG. 1 is a fragmentary elevational view, with parts broken away,showing one possible installation of the timing mechanism of theinvention in an artillery shell;

FIG. 2 is a front view of a timing mechanism in accordance with theinvention, with the usual front cover plate removed, shown in itsinitial unarmed condition;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2;

FIG. 4 is a view like that of FIG. 2, but showing the time delaymechanism after it has completed its motion to its armed condition;

FIG. 5 is a fragmentary view, taken like FIGS. 2 and 4, showing aportion of the timing mechanism as the second detent means thereof isreleased;

FIGS. 6, 7, 8, and 9. are enlarged fragmentary views, illustrating fourdifferent relative positions of the escapement teeth with respect to thepallet arrangement of the balance means, at four different correspondingangular positions of the balance means during its oscillation;

FIGS. 10, 11 and 12 are fragmentary sectional views taken along lines10-10, 11-11 and l2--12 of FIG. 2;

FIG. 13 is a perspective view of the pivot and pallet portions of thebalance means of FIG. 2;

FIG. 14 is an exploded fragmentary perspective view illustrating some ofthe parts of the first detent means employed in the arrangement of FIG.2;

FIG. 15 is a fragmentary exploded perspective view illustrating portionsof the second detent means employed in the construction of FIG. 2; and

FIG. 16 is a schematic view illustrating relative positions of thecenters of mass of rotor and balance, with respect to the pivot axis ofthe rotor and of the balance means and with respect to the spin axis ofthe entire mechanism, to which reference will be made in explaining theprinciple of the invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring now to the specificembodiments of the invention shown in the drawings by way of the exampleonly, FIG. 1 illustrates an explosive shell 10 containing as a componentthereof an arming delay-device 12 of a type using the apparatus of theinvention. The shell may be of the type comprising a main body portion14 containing a main explosive charge intended to explode in response toimpact of the firing pin 16 against the ground or similar object.Actuation of firing pin 16 by impact detonates the adjacent detonator 17to produce an impulse which, when the system is fully armed, travelsalong the interior of a flash tube 20 to the front surface of the delaydevice 12 and through a central opening in the delay device 12 to adetonator 21, which in turn explodes to detonate a booster-charge pellet22 and, in turn, the main explosive charge contained in the rear of theshell behind the booster cup 22A.

However, arming delay-device 12 has an unarmed condition in which thecentral opening through it is blocked and detonator 21 not aligned withbore 20, and contains a timing mechanism responsive to rotation of theshell to move progressively toward its armed position in which thecentral opening is unblocked and detonator 21 aligned with bore 20. Inuse, the arming delay device 12 in its unarmed condition is installed inthe shell before the shell is to be used and, when the shell is fired,the rotation of the shell due to the barrel rifling causes the armingdelay device to move progressively toward its armed condition and toreach the armed condition when the shell is at an appropriate distanceaway from the gun.

Typically the shell assembly may also comprise an auxiliary delayplunger assembly 23 which closes off communication between flash tube 20and delay device 12 until the shell begins to rotate in the gun, atwhich time assembly 23 is promptly actuated centrifugally to open thepath to delay device 12. Also sometimes employed is an interrupterassembly 24 which can be manually adjusted either to open the centralbore from the flash tube to the assembly 23, or to divert the explosiveimpulse through a parallel path (not shown) thereby to introduce afurther fixed delay in explosion of the shell.

In this example the timing mechanism is mounted within an outer housing32 having three progressively stepped outer diameters, the largestdiameter portion being externally threaded so as to mount the casingwithin the shell main body 14 by screw-threaded engagement therewith,and the smallest diameter portion being externally threaded to receiveand mount the booster cup 22A. The timing delay mechanism of theinvention is supported on a casing 32 positioned generally within theunthreaded casing portion 36 of intermediate diameter, by appropriatescrews such as 37 securing it to housing 31. It is this timing delaymechanism which is shown in the remaining figures and which constitutesone preferred embodiment of the present invention.

Since all of the FIGS. 2-17 relate to the same example of embodiment ofthe invention, corresponding parts in the various Figures are designatedby corresponding numerals.

Referring first particularly to FIGS. 2 and 3, showing the time delaymechanism in its completely unarmed condition as it would normallyappear when placed in an explosive shell prior to firing, it will beseen that the elements of the mechanism are mounted between the coverplates 38 and 40 by means of appropriate pivots and connectors. Moreparticularly, front cover plate 38 is held to a shoulder on a casing 32by screws such as 46. The mechanism includes an escapement rotor 48pivoted about an axis R and comprising a toothed escapement portion 50,a rotor weight 52 and a pivot 53 having stub shafts 54 and 55 at itsopposite ends fixed in corresponding holes in the front and rear coverplates, respectively. A sleeve bearing 55A integral with the rotorsurrounds the pivot 53 to permit turning of the rotor about its axis R.The detonator 21 is supported on the rear of the rotor in a closelyfitting cylinder 55B also integral with the rotor. The rotor axis R isdisplaced radially outwardly with respect to the central spin axis Sabout which the mechanism spins when the shell is fired from the gun. Inthis example spin axis S coincides with the longitudinal axis of thecylindrical casing 32. Furthermore, and as is particularly clearly shownin FIG. 16, the center of mass R of the rotor is displaced from itspivot axis R and, in the initial unarmed condition of the mechanismshown in FIGS. 2 and 16, is positioned other than directly radiallyoutward from the pivot axis R with respect to spin axis S, so that whenspinning of the mechanism occurs the centrifugal forces operating urgethe center of mass of the rotor from its initial position toward theposition in which it is radially outwardmost with respect to the spinaxis, i.e. toward a position on a straight line through the spin axis Sand the rotor axis R. Such spinning of the entire timing mechanismtherefore causes the rotor 48, when released, to rotate in thecounterclockwise direction as viewed in FIGS. 2 and 16, toward the armedposition shown in FIG. 4 in which detonator 21 is aligned with the spinaxis S and with openings 55C and 55D in the front and rear cover plates,respectively.

Initially such rotation of the rotor 48 is prevented by severalmechanisms. The first of these is a set-back arrangement, shownparticularly clearly in FIG. 10, comprising a set-back pin 56 springurged into a corresponding recess 58in the underside of a detent arm 64by means of a spring 60 acting between pin 56 and a spring washer 62secured in the rear cover plate 40. When the shell is fired, the forwardmotion of the shell and the inertia of the pin 56 cause the pin to bepulled backward, out of its recess, thus freeing the detent arm from theset-back mechanism. As will presently be explained, this permits lateroperation of the detent arm 64 in response to centrifugal forces. Suchset-back arrangements are well known in the prior art and need not bedescribed further herein.

Also initially restraining rotational motion of rotor 48 is a firstdetent means which include the above-mentioned detent arm 64 pivotedabout an axis 66 parallel to the spin axis S by means of a pivot 66A ona wall of the casing 32. The shape of this detent arm 60 is shownparticularly clearly in the exploded perspective view of FIG. 14. Thetip 67 of the detent arm 64 extends radially inwardly of the rotor,adjacent the shoulder 68 formed by a notch in the edge of .the rotor,and is normally so held by means of the flat-spring 70, one end of whichis secured in a slot 72 in the casing 32 and the other hooked end ofwhich is retained in a slot 74 in the detent arm 64. Detent arm 64 is soshaped and pivoted, and the flat-spring 70 so configured and mounted,that the spinning of the timing mechanism which occurs immediately afterfiring of the shell produces centrifugal forces on detent arm 64-, whosecenter of mass is ofi axis from its pivot axis 66, such that the latterarm rotates outwardly to the position thereof shown in FIG. 4, where thetip 67 of the detent arm no longer restrains the rotor 48 and insteadfrees it for subsequent rotation.

Also employed initially to restrain rotation of the rotor 48 are seconddetent means comprising detent arm 76, shown particularly clearly in theperspective view of FIG. 15, pivoted about a pivot axis 78 extendingparallel to spin axis S by means of a pivot 79 on the wall of the casing32. Detent arm 76 is biased radially inwardly by means of the flatspring 80 held at one end within a slot 82 in casing 32, and having anopposite hooked end held in a corresponding slot 83 in arm 76. The tip84 of detent arm 76 then abuts the shoulder 86 on the rim of rotor 48 toprevent it from executing its counterclockwise rotation. When the entiretiming delay mechanism is spun about spin axis S, the detent arm 76,which is pivoted off axis from its center of mass, is centrifugallyurged outwardly toward the position shown in FIG. 4. However, initiallydetent arm 76, is also prevented from rotating outwardly to free therotor 48 by a projection 88 integral with detent ann 76, whichencounters a shoulder 90 at one end of balance 92 when the detent arm 76attempts to rotate outwardly while the balance is in the position shownin FIG. 2. As will be described more fully hereinafter, before saidspinning begins, the balance 92 is held in the position shown in FIG. 2by a shoulder 94 formed by a notch at the opposite end of the balance,which bears against a corresponding downwardly extending shoulder 96 ondetent arm 64.

The balance 92 includes an integral pivot arrangement 98 shown inperspective in FIG. 13, on which are provided a pair of pallet horns 100and 102 which are engaged by the successive teeth such as 104 on theedge of rotor 48 when the rotor rotates, thereby to produce anoscillatory back-and-forth motion of balance 92 about the balance axisB. The pivot portion 98 of the balance includes a front pivot pin I06and a rear pivot pin 108, pivoted respectively in corresponding recessesin the front and rear cover plates 38 and 40. The large, generallycrescent-shaped mass of metal 110 constitutes the main balance weight.It is so configured and arranged that the center of mass B of the entirebalance means, including the balance weight portion and the pivot andpallet portions, is positioned radially inwardly toward the spin axis Swith respect to the pivot axis B of the balance means, as shownparticularly clearly in FIG. 16. As will be explained more fullyhereinafter, the effect of this arrangement is that, whenever in theoscillatory motion of the balance of center of mass departs from radialalingment with the pivot axis B of the balance and the spin axis, thespinning of the timing mechanism produces centrifugal forces tending torotate the balance means farther from its initial position of alignment,and this is taken advantage of in the present invention to enhance theslowing effect which the balance has on rotation of the rotor 48.

Also included on the rotor 38 in this embodiment of the invention is theratchet flat spring 1 14 extending generally tangent to the edge of therotor, but having a folded-under tab 116 extending under the rotor forsecuring the spring to the rotor in the position shown. When the rotorhas turned to its armed position as shown in FIG. 4, the shoulder 86thereon is stopped by a corresponding shoulder 118 formed on theinterior circumference of the casing 32; at this point the free end ofthe ratchet flat spring 114 has just passed the shoulder 120, alsoformed on the interior surface of the casing 32, so that the rotor isthereafter prevented from springing back rotationally in a clockwisedirection by abutment of the free end of the flat spring 114 againstshoulder 120.

In one use of the timing mechanism of the invention, it is placed in theunarmed condition illustrated in FIG. 2, with the set-back pin anddetent arms in their restraining positions to prevent rotation of therotor. Under these conditions the balance means 92 is held in an initialposition in which it and the pallet horns 100 and 102 are disposedsubstantially symmetrically about a radius from the spin axis S, asshown in FIG. 2. The pallet horns I and 102 then just bridge the tips ofthe first two of the teeth 104 on the edge of the rotor 48. Thisposition of the rotor is established by a shoulder 126 on the interiorof casing 32, which engages the trailing edge of the last of the teeth104, and maintained by the two detent arms 64 and 76. When in thiscondition, for the rotor 48 to be freed and possibly advanced toward thearmed position, it would be necessary to encounter shock and vibrationof a form which would draw the set-back pin 56 from the recess in thedetent arm 64, simultaneously to jar the first detent arm 64 outwardlyto free it from the rotor, cause the balance means 92 to rotatesufficiently clockwise to release the second detent arm 76, andthereafter provide a form of shock to move the second detent so it canmove to free rotor 48 therefrom, these conditions being maintainedsimultaneously while a force also occurs to effect a rotation of therotor 48. The possibilities of this occurring by chance are extremelyremote, particularly since a shock to be effective in releasing thesecond detent arm 76 must occur while the first detent arm is free ofthe rotor. Accordingly a high degree of safety is provided with respectto possible motion of the rotor toward an armed position in response toshock or vibration.

When the shell containing the timing mechanism is fired, the shell andtiming mechanism are accelerated longitudinally and spun about the spinaxis S by rifling on the interior of the gun barrel. Very early in thismotion, any of the auxiliary centrifugally operable safety devicesmentioned with respect to FIG. I are operated, the set-back pin 56 isretracted to release the detent arm 64 from it, and the first detent arm64 is rotated outwardly to the position shown in FIG. 4 by centrifugalforces acting against the flat spring 70. When this occurs, the rotor 48begins to rotate counterclockwise and the first tooth thereon actsagainst pallet horn to turn the balance means 92 slightly clockwise tothe position illustrated in FIG. 5, permitting the second detent arm 76to respond to centrifugal forces and move outwardly through the positionshown in FIG. 5 to the position shown in FIG. 4, whereafter the rotor 48is free to rotate except for the resisting effects of oscillation of thebalance means 92.

FIG. 6 illustrates successive relative positions of the escapement teeth104 and the pallet horns 100 and 102 during this first rotational motionof rotor 48. As mentioned previously, in this example the horns arespaced about 1 A times the distance between the peaks of the teeth 104so as to bridge the peaks of two adjacent teeth, although other hornspacings may be used instead. At the point in the cycle shown in FIG. 6,the center of mass of the entire balance means has been moved away froma radius through balance pivot axis B, and centrifugal forces aretherefore urging the balance means in a clockwise direction. However,shortly after the peak of the first tooth passes beyond pallet horn I00,pallet horn 102 encounters the leading edge of the third tooth, therebyarresting further clockwise angular rotation of the balance means. Whileunder this momentary condition the centrifugal forces acting on thebalance means tend to accelerate the rotor 48, this condition lasts onlybriefly, since very shortly thereafter the peak of the third escapementtooth forces the balance means to rotate counterclockwise to theposition shown in FIG. 8, against the torque produced by centrifugalforces acting on the center of mass of the balance means. Accordingly,during this phase of operation, the centrifugal forces acting on thebalance means exert strong retarding torques on the rotor 48, slowingits movement accordingly. This continues until the balance has turnedsufficiently counter-clockwise so that the center of mass is now on theopposite side of a radius through the balance pivot axis B, and shortlythereafter the horn 100 falls against the leading edge of the secondescapement tooth and, again by camming action, the balance means isforced by that tooth to rotate clockwise against centrifugal forcesacting on the center of mass of the balance as illustrated in FIG. 9.

The net effect of this arrangement is that the rotary motion of therotor is resisted not only by the inertia of the balance as it isaccelerated during its oscillatory motion, but is further resisted bytorques exerted on the rotor by the pallet hornsin response tocentrifugal forces acting on the center of mass of the balance duringportions of its cycle of oscillation due to displacement of said centerof mass from the pivot axis of the balance. This results in asubstantial increase in the slowing effect on the rotor obtainable witha given mass and inertial moment of balance, and in practicalarrangements has been found also to make possible the elimination of theusual intermediate gear train which has sometimes been used in an effortfurther to slow the motion of the rotor. Accordingly, an arming delay ofsufficient duration is provided in this relatively simple, compact andlightweight timing mechanism to permit the fuse to become armed onlywhen the shell is well away from the gun, as desired.

This motion of the rotor and the oscillation of the balance meanscontinues until all the escapement teeth have passed through the horns,after which the rotor drops free for the remaining angular travel untilthe detonator 21 is aligned with the spin axis and with the openings inthe front and rear cover plates of the timing mechanism, i.e. until thearmed state is attained. As mentioned previously, at this time the freeend of the ratchet flat spring 114 has passed the shoulder 120,preventing any substantial back-lash or counterclockwise motion of therotor after it is arrested by striking the stopping shoulder 118,thereby to assure that the rotor remains in the angular positioncorresponding to arming.

While in the interest of definiteness the invention has been describedwith particular reference to specific forms thereof, it will beunderstood that it can be embodied in a variety of forms differingsubstantially from those specifically shown and described, withoutdeparting from the scope of the invention as defined by the appendedclaims.

What is claimed is:

1. In a centrifugally operable arming delay mechanism comprising acentrifugally operable rotor rotatable between an initial unarmedposition and a final armed position in response to spinning of saidmechanism about an axis therein, and first centrifugally operable detentmeans for preventing rotation of said rotor prior to said spinning butresponsive to said spinning to move so as to free said rotor therefrom,the improvement comprising:

second centrifugally operable detent means for preventing rotation ofsaid rotor prior to said spinning but responsive to said spinning, whenreleased, to move so as to free said rotor therefrom; and

interlock means acting between said first and second detent means forrestraining said second detent means until said first detent means hasmoved to free said rotor therefrom, and for releasing said second detentmeans in response to said moving of said first detent means, thereby topermit subsequent freeing of said rotor from said second detend means.

2. Apparatus in accordance with claim 1, in which said interlock meanscomprises balance means responsive to rotation of said rotor tooscillate about a pivot axis therein thereby to slow said rotation ofsaid rotor, said balance means extending between said first and seconddetent means and configured and held by said first detent means prior tosaid spinning to restrain said second detent means from moving so as tofree said rotor from said second detent means, said moving of said firstdetent means to free said rotor therefrom permitting said balance meansto move in response to said rotor thereby permitting said second detentmeans to move so as to free said rotor therefrom.

3. Apparatus in accordance with claim 2, in which said pivot axis ofsaid balance means is farther from said axis of spinning than is thecenter of mass of said balance means.

4. In a centrifugally operable arming delay mechanism for a projectilewhich spins about a predetermined spin axis therein after firing of theprojectile, and comprising a pivoted balance, a rotor pivoted off-centerfrom its center of mass and from said spin axis so as to rotate, whenfree, in response to centrifugal forces generated by such spinning ofsaid projectile, toothed means connecting said rotor to said balance tocause said balance to oscillate and to slow said rotation of said rotor,and first centrifugally operable detent means having a first position inwhich it normally blocks said rotation of said rotor and a secondposition to which it is operable in response to said spinning in whichsaid rotor is freed of said first detent means, the improvement inaccordance with which:

said mechanism comprises second centrifugally operable detent meanshaving a first position in which it normally blocks said rotation ofsaid rotor and a second position toward which it is urged by centrifugalforces during said spinning and in which said rotor is freed of saidsecond detent means, said balance means being configured to extendbetween said first and second detent means and having restraining meansthereon for holding said second detent means in said first positionthereof despite said urging by said centrifugal forces when said balancemeans is in one rotational position thereof and for freeing said seconddetent means when said balance is in a second rotational positionthereof, and releasable means for holding said balance means in saidfirst position prior to said spinning and responsive to movement of saidfirst detent means from said first position thereof to said secondposition thereof to release said releasable means and thereby permitsaid balance means to assume said second position thereof, whereby saidspinning causes said rotor to be freed of said second detent only aftersaid rotor has been freed from said first detent.

5. Apparatus in accordance with claim 4, in which said balance means ispivoted about an axis further from said spin axis than is the center ofmass of said balance means.

6. In a centrifugally operated time-delay mechanism for a projectile ofthe type which spins about a predetermined axis after firing, therebyalso to spin said mechanism about a spin axis in said mechanism, andcomprising centrifugally operated rotor means and escapement meansincluding a pivoted balance means for resisting and slowing theoperation of said escapement means and said rotor means, the improvementaccording to which said balance means has a pivot axis which is furtherfrom said spin axis than is the center of mass of said balance means,whereby centrifugal forces acting on said balance means due to spinningof said mechanism about said spin axis produce a decrease in the rate ofrotation of said rotor means.

7. Apparatus in accordance with claim 6, in which said escapement meanscomprises a plurality of teeth integral with said rotor means and saidbalance means comprises pallet means engaged successively by differentones of said teeth as said rotor means rotates to cause said balancemeans to oscillate about said pivot axis.

8. A rotation-responsive runaway-escapement time-delay mechanism,comprising:

a support rotatable about a first axis therein;

a centrifugally operable rotor pivoted about a second axis displacedfrom said first axis and having a center of mass displaced from saidsecond axis, whereby rotation of said support about said first axisurges said rotor centrifugally toward an outwardmost angular position inwhich said center of mass is at its maximum distance from said firstaxis;

balance wheel teeth mechanically connected in torquetransmittingrelation with said rotor so as to rotate with rotation of said rotor andso as to respond to torques applied to said teeth to accelerate ordecelerate rotation of said rotor toward said outward-most position; and

balance means pivoted about a third axis and having a center of massdisplaced radially inwardly from said third axis toward said first axis,said balance means comprising pallet means positioned to be engaged bysuccessive ones of said balance wheel teeth as said rotor rotates aboutsaid second axis toward said outwardmost angular position so as tooscillate said balance means about said pivot means in response tomotion of said teeth and in response to centrifugal force due torotation of said support, thereby to slow the rotation of said rotortoward said outwardmost angular position.

9. In a centrifugally operated time-delay arming mechanism for use in anexplosive shell to delay the arming of said shell until after it hasbeen fired and has executed a predetermined number of revolutions ofspin about a spin axis extending through said mechanism, said mechanismcomprising:

a centrifugally operable rotor mounted to pivot about a first axisdisplaced from said spin axis and having a center of mass displaced fromsaid first axis whereby spinning of said mechanism about said spin axisurges said rotor from an unarmed angular position in which said centerof mass is relatively nearer said spin axis toward an armed angularposition in which said center of mass is relatively farther from saidspin axis; camming teeth on said rotor; and balance means mounted topivot about a second axis displaced from said first axis and from saidspin axis and positioned to oscillate back and forth about said secondaxis in response to engagement by successive ones of said camming teethas said rotor moves toward said armed position;

the improvement wherein said balance means has a center of mass nearersaid spin axis than is said second axis, whereby the oscillations ofsaid balance means are opposed at least in part by centrifugal forcesacting on said balance means in response to rotation of said mechanismabout said spin axis.

1. In a centrifugally operable arming delay mechanism comprising a centrifugally operable rotor rotatable between an initial unarmed position and a final armed position in response to spinning of said mechanism about an axis therein, and first centrifugally operable detent means for preventing rotation of said rotor prior to said spinning but responsive to said spinning to move so as to free said rotor therefrom, the improvement comprising: second centrifugally operable detent means for preventing rotation of said rotor prior to said spinning but responsive to said spinning, when released, to move so as to free said rotor therefrom; and interlock means acting between said first and second detent means for restraining said second detent means until said first detent means has moved to free said rotor therEfrom, and for releasing said second detent means in response to said moving of said first detent means, thereby to permit subsequent freeing of said rotor from said second detend means.
 2. Apparatus in accordance with claim 1, in which said interlock means comprises balance means responsive to rotation of said rotor to oscillate about a pivot axis therein thereby to slow said rotation of said rotor, said balance means extending between said first and second detent means and configured and held by said first detent means prior to said spinning to restrain said second detent means from moving so as to free said rotor from said second detent means, said moving of said first detent means to free said rotor therefrom permitting said balance means to move in response to said rotor thereby permitting said second detent means to move so as to free said rotor therefrom.
 3. Apparatus in accordance with claim 2, in which said pivot axis of said balance means is farther from said axis of spinning than is the center of mass of said balance means.
 4. In a centrifugally operable arming delay mechanism for a projectile which spins about a predetermined spin axis therein after firing of the projectile, and comprising a pivoted balance, a rotor pivoted off-center from its center of mass and from said spin axis so as to rotate, when free, in response to centrifugal forces generated by such spinning of said projectile, toothed means connecting said rotor to said balance to cause said balance to oscillate and to slow said rotation of said rotor, and first centrifugally operable detent means having a first position in which it normally blocks said rotation of said rotor and a second position to which it is operable in response to said spinning in which said rotor is freed of said first detent means, the improvement in accordance with which: said mechanism comprises second centrifugally operable detent means having a first position in which it normally blocks said rotation of said rotor and a second position toward which it is urged by centrifugal forces during said spinning and in which said rotor is freed of said second detent means, said balance means being configured to extend between said first and second detent means and having restraining means thereon for holding said second detent means in said first position thereof despite said urging by said centrifugal forces when said balance means is in one rotational position thereof and for freeing said second detent means when said balance is in a second rotational position thereof, and releasable means for holding said balance means in said first position prior to said spinning and responsive to movement of said first detent means from said first position thereof to said second position thereof to release said releasable means and thereby permit said balance means to assume said second position thereof, whereby said spinning causes said rotor to be freed of said second detent only after said rotor has been freed from said first detent.
 5. Apparatus in accordance with claim 4, in which said balance means is pivoted about an axis further from said spin axis than is the center of mass of said balance means.
 6. In a centrifugally operated time-delay mechanism for a projectile of the type which spins about a predetermined axis after firing, thereby also to spin said mechanism about a spin axis in said mechanism, and comprising centrifugally operated rotor means and escapement means including a pivoted balance means for resisting and slowing the operation of said escapement means and said rotor means, the improvement according to which said balance means has a pivot axis which is further from said spin axis than is the center of mass of said balance means, whereby centrifugal forces acting on said balance means due to spinning of said mechanism about said spin axis produce a decrease in the rate of rotation of said rotor means.
 7. Apparatus in accordance with claim 6, in which said escapement means comprises a plurality of teetH integral with said rotor means and said balance means comprises pallet means engaged successively by different ones of said teeth as said rotor means rotates to cause said balance means to oscillate about said pivot axis.
 8. A rotation-responsive runaway-escapement time-delay mechanism, comprising: a support rotatable about a first axis therein; a centrifugally operable rotor pivoted about a second axis displaced from said first axis and having a center of mass displaced from said second axis, whereby rotation of said support about said first axis urges said rotor centrifugally toward an outwardmost angular position in which said center of mass is at its maximum distance from said first axis; balance wheel teeth mechanically connected in torque-transmitting relation with said rotor so as to rotate with rotation of said rotor and so as to respond to torques applied to said teeth to accelerate or decelerate rotation of said rotor toward said outward-most position; and balance means pivoted about a third axis and having a center of mass displaced radially inwardly from said third axis toward said first axis, said balance means comprising pallet means positioned to be engaged by successive ones of said balance wheel teeth as said rotor rotates about said second axis toward said outwardmost angular position so as to oscillate said balance means about said pivot means in response to motion of said teeth and in response to centrifugal force due to rotation of said support, thereby to slow the rotation of said rotor toward said outwardmost angular position.
 9. In a centrifugally operated time-delay arming mechanism for use in an explosive shell to delay the arming of said shell until after it has been fired and has executed a predetermined number of revolutions of spin about a spin axis extending through said mechanism, said mechanism comprising: a centrifugally operable rotor mounted to pivot about a first axis displaced from said spin axis and having a center of mass displaced from said first axis whereby spinning of said mechanism about said spin axis urges said rotor from an unarmed angular position in which said center of mass is relatively nearer said spin axis toward an armed angular position in which said center of mass is relatively farther from said spin axis; camming teeth on said rotor; and balance means mounted to pivot about a second axis displaced from said first axis and from said spin axis and positioned to oscillate back and forth about said second axis in response to engagement by successive ones of said camming teeth as said rotor moves toward said armed position; the improvement wherein said balance means has a center of mass nearer said spin axis than is said second axis, whereby the oscillations of said balance means are opposed at least in part by centrifugal forces acting on said balance means in response to rotation of said mechanism about said spin axis. 